Kayaking on the Hiwassee River was one of the coolest things we've ever done. We went with Hiwassee Outfitters, who provided us with Dagger Torrent 10.0 sit-on-top kayaks and transportation upriver for $30 each. When you add in the 10% TN sales tax and multiply it by the two of us, this ended up being about the most expensive thing we did on our Gatlinburg trip, but it was worth every penny.
The Hiwassee is deep and crystal clear. The outfitter's website says the water is about 54 degrees; it was indeed cold, but it didn't seem quite that cold, maybe because it was a 90-degree day. But in any case, we were hopping off the kayaks and into the water to swim quite a bit. This was the first time we'd used sit-on-top kayaks, and they're definitely far easier to get into (onto), out of, and back into again than sit-in kayaks. These kayaks also spin far more easily than our recreational kayaks: with a single paddle stroke, you can easily do a 180, and about a full 360 if you try hard enough. Of course they're somewhat harder to control because of this: you need to paddle constantly or else you get turned sideways/backwards automatically. But that's not really a problem as long as you've got some stretches of flat water between the rapids, which the Hiwassee does.
The day we kayaked was a 2-generator day at the Apalachia Dam, which is just upstream from where we put in, which means the water level was somewhat higher than on a 1-generator day. The rapids on this section include class I, II, and III (the first II or III we've ever done) depending on the water level, but so far I haven't been able to find which rapids classes correspond to what water levels. Of course never having been there before, we had no way to compare the levels, but on this day there were spots that were just a foot or two deep, and other spots that were 8+ feet deep. The really neat thing was that, because the water was so clear, we were able to see all these awesome rock formations going deep under the water and passing by underneath us the whole time.
Our 5.5-mile trip took 2 hours, and our only complaint is that it wasn't longer! If we're ever back in this area again, we'll definitely make a point to kayak the Hiwassee again.